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Surveys of Mississippi rice growers indicate that nearly 40 percent believe they have herbicide-resistant barnyardgrass in their fields, says Jason Bond. For best results with barnyardgrass, he told growers at the annual Delta Ag Expo, growers should start with clean fields, and “treat early and often.”

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Tailor nitrogen rate to variety

Many growers may need to rethink their rice fertilization strategy, says Tim Walker, associate research professor at the Delta Research and Extension Center.

“We’ve tended to get into the mindset that rice nitrogen response is linear,” he said at the Delta Ag Expo. “But that’s not so — it’s actually curvilinear.”

Researchers are finding, he says, that reducing N rates can, in many cases, reduce production costs without yield loss. And applying excess N can reduce, rather than boost, rice yield; with some varieties, too much N can also increase lodging.

While some varieties can tolerate N rates as high as 240 lbs. per acre without lodging, he says, others will have lodging at rates over 135 pounds.

“We need a more precise way to prescribe N rates,” Walker says, “so we don’t over- or under-fertilize rice. The N-ST*R test, developed by the University of Arkansas, shows tremendous promise in providing the accuracy and precision we need.”

The test allows growers to make fertilizer decisions based on knowledge of how much N is supplied by soils on their farm. The results may be greater or less than current state average rates.

Although N-ST*R is not yet commercially available, Walker says work is continuing to validate the models.

Commenting on nitrogen stabilizers, he says, “There are a lot of these products, but the only one we’ve found that will stabilize nitrogen from volatility losses is Agrotain.”

With Agrotain, he notes, urea loses only about 7 percent of its effectiveness to volatility, compared to as much as 40 percent for urea alone.

“With urea at $400-plus per ton, unless you can flood quickly, I would suggest using Agrotain.”